The e-book business is growing rapidly, with new ventures being launched and established ones seeing impressive growth.

E-reader sales increased across the U.S. over the holidays, with Amazon selling millions of Kindles in a week; Barnes & Noble seeing its Nook business increase 70 percent; and Kobo customer sign-ups increasing 10 times, Mediabistro reported.

New ventures are on the horizon as well. Former Seattle Post-Intelligencer chief Michelle Nicolosi is launching her own e-book publishing business, called Working Press, Geek Wire reported today. Working Press will “edit, format, publish, distribute and market the work of journalists and other established writers.”

Established bookseller Barnes & Noble announced it may spin off its Nook business from the rest of the company, paidContent reported today. The Nook branch is expected to reach US$1.5 billion in 2012.

“We see substantial value in what we’ve built with our Nook business in only two years, and we believe it’s the right time to investigate our options to unlock that value,” said B&N CEO William Lynch.